I think it is more a matter of different playstyles rather than a difference in strength. The Lieutenant for example has a Stuart, where the Captain has a weaker Greyhound. The Cavalry Riflemen are specific separated from Assault Engineers because they are both close range units. But also Rangers and Cavalry Riflemen as both elite infantry should not be together.

The two tiers are carefully designed where overlapping roles are separated. Swapping only two units won't improve the two tiers overall.

In case of anti tank power: The Lieutenant has a bazooka upgrade, the M3 can deploy bazooka's in the field and the Stuart can handle all early game vehicles. Also like you mentioned, the Cavalry Riflemen have the AT satchel. Maybe a commander which provides the Ranger call-in is a solution for you.

The lieutenant IMO is one of the best support units because he's primarily an early AT squad that provides great synergies with Cavalry. If you wanted to stop the non-sense of 221 Half-tracks or Scout Cars then the lieutenant is your go-to squad and is a fundamental must-have in the USF's lineup.

His incredibly cheap buff and when paired with Cavalry's anti-vehicle satchel charge, provides an exceptional AT alternative that's extremely cost effective.
Consider that the Lieutenant is given the "Combined Arms" ability, and it's very much clear that his forte stands to accomodate mechanized warfare.
Having an M3 Half-track (which you should always have on the field FYI)
carrying both a Lieutenant and Cavalry Squad is one of the most effective and self-sustaining expeditionary forces you can throw into a situation.

If anything, my opinion is frankly the opposite with the Captain's only real use to me being his "On Me" ability. Being able to remove squad suppression and give them some additional buffs is nice but given how it's limited to only one squad while the Lieutenant can affect as many as he wants and stack it with Combined Arms; the Cap feels lackluster in overall effectiveness where I either pair him with BAR Riflemen or M1919A6 Rangers.
I guess it fits his defensive tech pathway but by the same token, how does his ability make sense then? If he's gonna be on the defensive, why is he given a rather mediocre offensive rush ability, especially if he's got access to smoke grenades.

I can see some synergies with both the smoke and "on me" but it feels FAR too situational compared to the amount of utility and potential the Lieutenant has.
If the M1 AT wasn't in his tech tree, I wouldn't buy the captain for any reason at all.
Maybe Rangers? But I'd go straight to Major who has significantly more utility from artillery to recon and forward retreat.

The M3 Half-Track with Cavalry in them hard-counters the MG because it can bypass the suppression altogether and rip it apart at point blank so subjecting the Captain and his Rangers to hostile fire and risk getting hit with explosives just isn't worth it.

I just don't see much value in Rangers when the Lieutenant and his escort of chad Cavalrymen can hold their own against both vehicles, trenches, tanks and infantry.
Sure the Rangers get 3 weapon slots with far better stats but the benefits feel so marginal in practice that I never saw the necessity for them other than manpower filler.